Semiconductor switching circuits have been proposed in which a network is provided which protects the semiconductor power switch, for example a switching transistor, and which includes a capacitor, a diode, and a resistor network. Power which is dissipated within the semiconductor switch upon changing between conductive and non-conductive state is thereby reduced, so that a given semiconductor can be used to switch higher currents, or switch at higher voltage levels, than possible without the auxiliary protective network. The switching power which arises upon changing state by the semiconductor is transferred, at least in part, into the resistor or resistors of the switching network and dissipated therein in the form of heat. This arrangement, thus, transfer switching losses from the semiconductor to an element which is more susceptible to head radiation. Yet, the commutating energy which arises within the semiconductor switch upon each switching event is dissipated in the resistors. and hence wasted. Each one of the semiconductor switches requires its own protective and heat dissipating network.
Bilateral switching circuits have been proposed in which direct current is connected to a load to flow, respectively, in reverse directions. Typically, such a load is a motor, or a portion thereof, for example the armature or the field, and the load, thus, is inductive. Typically, two semiconductor switching elements are used, each with its own protective or power dissipating network, one, each, connected into a main line to the load and controlling current flow in a respective direction thereto.